蚂蚁的巢穴包括：

• 有限数量的蚂蚁；
• 巢穴的位置，可以由本身控制也可以从world对象控制；
• 巢穴的样子，就是图片的设置；
• 巢穴中蚂蚁找到的食物的数量

import greenfoot.*;  // (World, Actor, GreenfootImage, and Greenfoot)
 
/**
 * A hill full of ants.
 *
 * @author Michael Kolling
 * @version 1.1
 */
public class AntHill extends Actor
{
    /** Number of ants that have come out so far. */
    private int ants = 0;
 
    /** Total number of ants in this hill. */
    private int maxAnts = 40;
 
    /** Counter to show how much food have been collected so far. */
    private Counter foodCounter;
 
    /**
     * Constructor for ant hill with default number of ants (40).
     */
    public AntHill()
    {
    }
 
    /**
     * Construct an ant hill with a given number of ants.
     */
    public AntHill(int numberOfAnts)
    {
        maxAnts = numberOfAnts;
    }
 
    /**
     * Act: If there are still ants left inside, see whether one should come out.
     */
    public void act()
    {
        if(ants < maxAnts)
        {
            if(Greenfoot.getRandomNumber(100) < 10)
            {
                getWorld().addObject(new Ant(this), getX(), getY());
                ants++;
            }
        }
    }
 
    /**
     * Record that we have collected another bit of food.
     */
    public void countFood()
    {
        if(foodCounter == null)
        {
            foodCounter = new Counter("Food: ");
            int x = getX();
            int y = getY() + getImage().getWidth()/2 + 8;
 
            getWorld().addObject(foodCounter, x, y);
        }
        foodCounter.increment();
    }
}

上面AntHill中提到一个Counter类，介绍一下他的实现：

返回

import greenfoot.*;  // (World, Actor, GreenfootImage, and Greenfoot)
 
/**
 * Counter that displays some taxt and a number.
 *
 * @author Michael Kolling
 * @version 1.1
 */
public class Counter extends Actor
{
    private int value = 0;
    private String text;
 
    /**
     * Create a counter without a text prefix, initialized to zero.
     */
    public Counter()
    {
        this("");
    }
 
    /**
     * Create a counter with a given text prefix, initialized to zero.
     */
    public Counter(String prefix)
    {
        text = prefix;
        int imageWidth= (text.length() + 2) * 10;
        setImage(new GreenfootImage(imageWidth, 16));
        updateImage();
    }
 
    /**
     * Increment the counter value by one.
     */
    public void increment()
    {
        value++;
        updateImage();
    }
 
    /**
     * Show the current text and count on this actor's image.
     */
    private void updateImage()
    {
        GreenfootImage image = getImage();
        image.clear();
        image.drawString(text + value, 1, 12);
    }
}